Customized intervertebral prosthetic disc with shock absorption

ABSTRACT

A prosthesis system comprises plates that can be positioned against vertebrae and a selected resilient core that can be positioned between the plates to allow the plates to articulate. The selected resilient core can be chosen from a plurality of cores in response to patient characteristics, such as age and/or intervertebral mobility, such that the prosthesis implanted in the patient is tailored to the needs of the patient. The plurality of cores may comprise cores with different resiliencies, and one of the cores can be selected such that the upper and lower plates articulate with the desired shock absorbing resiliency and/or maximum angle of inclination when the one selected core is positioned between the plates.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 13/941,121 (Attorney Docket No. 29850-717.402), filed Jul. 12,2013, which is a divisional of U.S. patent application Ser. No.12/883,068 (Attorney Docket No. 29850-717.401), filed Sep. 15, 2010, nowU.S. Pat. No. 8,506,631, which is a divisional of U.S. patentapplication Ser. No. 11/836,684 (Attorney Docket No. 29850-717.201),filed Aug. 9, 2007; the full disclosures of each are incorporated hereinby reference in its entirety.

BACKGROUND OF THE INVENTION

The present invention relates to medical devices and methods. Morespecifically, the invention relates to intervertebral disc prostheses.

Back pain takes an enormous toll on the health and productivity ofpeople around the world. According to the American Academy of OrthopedicSurgeons, approximately 80 percent of Americans will experience backpain at some time in their life. In just the year 2000, approximately 26million visits were made to physicians' offices due to back problems inthe United States. On any one day, it is estimated that 5% of theworking population in America is disabled by back pain.

One common cause of back pain is injury, degeneration and/or dysfunctionof one or more intervertebral discs. Intervertebral discs are the softtissue structures located between each of the thirty-three vertebralbones that make up the vertebral (spinal) column. Essentially, the discsallow the vertebrae to move relative to one another. The vertebralcolumn and discs are vital anatomical structures, in that they form acentral axis that supports the head and torso, allow for movement of theback, and protect the spinal cord, which passes through the vertebrae inproximity to the discs.

Discs often become damaged due to wear and tear or acute injury. Forexample, discs may bulge (herniate), tear, rupture, degenerate or thelike. A bulging disc may press against the spinal cord or a nerveexiting the spinal cord, causing “radicular” pain (pain in one or moreextremities caused by impingement of a nerve root). Degeneration orother damage to a disc may cause a loss of “disc height,” meaning thatthe natural space between two vertebrae decreases. Decreased disc heightmay cause a disc to bulge, facet loads to increase, two vertebrae to rubtogether in an unnatural way and/or increased pressure on certain partsof the vertebrae and/or nerve roots, thus causing pain. In general,chronic and acute damage to intervertebral discs is a common source ofback related pain and loss of mobility.

When one or more damaged intervertebral discs cause a patient pain anddiscomfort, surgery is often required. Traditionally, surgicalprocedures for treating intervertebral discs have involved discectomy(partial or total removal of a disc), with or without fusion of the twovertebrae adjacent to the disc. Fusion of the two vertebrae is achievedby inserting bone graft material between the two vertebrae such that thetwo vertebrae and the graft material grow together. Oftentimes, pins,rods, screws, cages and/or the like are inserted between the vertebraeto act as support structures to hold the vertebrae and graft material inplace while they permanently fuse together. Although fusion often treatsthe back pain, it reduces the patient's ability to move, because theback cannot bend or twist at the fused area. In addition, fusionincreases stresses at adjacent levels of the spine, potentiallyaccelerating degeneration of these discs.

In an attempt to treat disc related pain without fusion, an alternativeapproach has been developed, in which a movable, implantable, artificialintervertebral disc (or “disc prosthesis”) is inserted between twovertebrae. A number of different intervertebral disc prostheses arecurrently being developed. For example, the inventors of the presentinvention have developed disc prostheses described in U.S. patentapplication Ser. Nos. 10/855,817 and 10/855,253, previously incorporatedby reference. Other examples of intervertebral disc prostheses are theLINK® SB Charite disc (provided by DePuy Spine, Inc.) Mobidisk®(provided by LDR Medical (www.ldrmedical.fr)), the Bryan Cervical Disc(provided by Medtronic Sofamor Danek, Inc.), the ProDisc® or ProDisc-C®(from Synthes Stratec, Inc.), and the PCM disc (provided by Cervitech,Inc.). Although existing disc prostheses provide advantages overtraditional treatment methods, improvements are ongoing.

Work in relation to the present invention suggests that currentprosthesis and methodologies may be less than ideal. For example, somedisc prostheses may only partially restore patient motion in somepatients. Also, some disc prostheses may potentially provide more motionpostoperatively than might occur naturally for an individual patient,depending on his or her individual characteristics. For example, olderpatients may have a smaller range of motion between vertebrae thanyounger patients, and a prosthesis with an appropriate range of motionfor a younger patient may provide an excessive range of motion for anolder patient. Younger active patients may place a greater load on adisc prosthesis, and current prostheses may be less than ideal forrestoring motion between the vertebrae in a manner that fullyaccommodates such active patients.

Therefore, a need exists for improved intervertebral disc prostheses.Ideally, such improved prostheses would avoid at least some of the shortcomings of the present prostheses.

BRIEF SUMMARY OF THE INVENTION

Embodiments of the present invention provide customizable intervertebralprostheses systems and methods. The prosthesis system comprises supportsthat can be positioned against vertebrae and a selected resilient corethat can be positioned between the supports to allow the supports toarticulate. The resilient core can be selected from a plurality of coresin response to patient characteristics, such as age and/orintervertebral mobility, such that the prosthesis implanted in thepatient is tailored to the needs of the patient. The plurality of corescomprise cores with different resiliencies, and one of the cores can beselected such that the upper and lower supports articulate with thedesired shock absorbing resiliency and/or maximum angle of inclinationwhen the selected core is positioned between the supports. The shockabsorbing core may be compressed during insertion into theintervertebral space to minimize distraction between the vertebrae. Thesupports can comprise known support plates and may comprise, in someembodiments, in situ expandable supports to minimize the invasiveness ofthe procedure.

In a first aspect an intervertebral disc prosthesis system is provided.The system comprises a plurality of selectable cores. Each corecomprises upper and lower surfaces and at least one of a resilientmaterial or a resilient member disposed between the upper and lowersurfaces to allow the upper and lower surfaces to move resilientlytoward and away from each other. The system also comprises upper andlower supports that are locatable about the core. Each support comprisesan outer surface which engages a vertebra and an inner surface that isshaped to contact one of the surfaces of each core. Each core of theplurality comprises a different resiliency. The upper and lower supportsare adapted to articulate when one of the cores is selected andpositioned between the upper and lower supports.

In many embodiments, each core is identifiable with an indicia, suchthat each core is selectable in response to the indicia and a patientcharacteristic. The indicia may comprise at least one of a color of thecore, a marking on the core, a height of the core, or a width of thecore. In specific embodiments, the indicia of each core corresponds to aresiliency of the core and a maximum angle of inclination between thesupports when the core is positioned between the supports.

In many embodiments, each core of the plurality comprises a differentdimension to limit a maximum angle of inclination between the upper andlower supports in response to the patient characteristic. The differentdimension may comprise at least one of a height or a width.

In many embodiments, the upper surface of each core comprises a curvedsurface to slide against the inner surface of the upper support. Inspecific embodiments, lower surface of each core may be capable ofattachment to the lower support. In some embodiments, the lower surfaceof each core comprises a curved surface to slide against the innersurface of the lower support.

In many embodiments, each core comprises an upper component with theupper surface disposed thereon and a lower component with the lowersurface disposed thereon. The upper and lower core components of eachcore can be configured to slide relative to one another in response toloading when positioned between the upper and lower supports, forexample loading caused by patient activity. In specific embodiments, theupper and lower components of each core are configured to slide relativeto one another with telescopic motion.

In some embodiments, the upper support comprises a upper plate and thelower support comprises a lower plate.

In some embodiments, the upper support comprises an upper expandablesupport and the lower support comprises a lower expandable support.

In some embodiments, several cores of the plurality comprises the sameheight and different resiliencies, such that a maximum angle ofinclination between the plates is substantially the same for the severalcores.

In many embodiments, the plurality of selectable cores comprises coreswith a maximum compression within a range from about ⅓ mm to about 1 mm.

In another aspect, an intervertebral disc prosthesis system is provided.The intervertebral disc prosthesis system comprises a plurality ofselectable cores. Each core comprises upper and lower curved surfaces.At least one of a resilient material or a resilient member is disposedbetween the upper and lower curved surfaces to allow the upper and lowersurfaces to move resiliently toward and away from each other. The systemalso comprises upper and lower supports that are locatable about thecore. Each support comprises an outer surface, which engages a vertebra,and an inner curved surface shaped to slide over one of the curvedsurfaces of each core. Each core of the plurality comprises a differentresiliency. The upper and lower supports are adapted to articulate whenone of the cores is selected and positioned between the upper and lowersupports.

In many embodiments, each core is identifiable with an indicia, suchthat each core is selectable in response to the indicia and a patientcharacteristic. The indicia may comprise at least one of a color of thecore, a marking on the core, a height of the core, or a width of thecore. In specific embodiments, the indicia of each core corresponds to aresiliency of the core and a maximum angle of inclination between thesupports when the core is positioned between the supports.

In many embodiments, the at least one resilient material comprises apolymer. The at least one resilient material may comprise a hydrogel.The at least one resilient support member may be disposed within theresilient material and attached to the upper and lower curved surfaces.

In many embodiments, the at least one resilient support member comprisesa plurality of springs.

In many embodiments, the upper and lower curved surfaces of the corecomprise at least one of a polymer, a ceramic and a metal. The metal maycomprise at least one of cobalt chrome molybdenum, titanium or stainlesssteel.

In another aspect, a method of assembling an intervertebral prosthesisfor insertion into a patient is provided. A resilient core is selectedfrom among a plurality of resilient cores. The core is placed betweenfirst and second supports. The core is selected in response to aresiliency of the core and a patient characteristic.

In many embodiments, the selected core is identified with an indicia andselected in response to the indicia and a patient characteristic. Theindicia may comprise at least one of a color of the core, a marking onthe core, a height of the core, or a width of the core. In specificembodiments, the indicia of each core corresponds to a resiliency of thecore and a maximum angle of inclination between the supports when thecore is positioned between the supports.

In many embodiments, the first and second supports articulate when thecore is positioned between the supports. The core may comprise first andsecond components that slide relative to each other when the core isloaded.

In many embodiments, the core is selected in response to a maximum angleof inclination when the core is positioned between the supports.

In another aspect, a method of inserting an intervertebral prosthesisinto an intervertebral space between vertebrae of a patient is provided.A shock absorbing core is compressed from an expanded profileconfiguration to a narrow profile configuration when the core isinserted into the intervertebral space. The shock absorbing core canarticulate an upper support and a lower support when positioned betweenthe upper support and the lower support.

In many embodiments, the upper support and the lower support arepositioned in the intervertebral space, and the shock absorbing core isinserted between the upper support and the lower support while the uppersupport and the lower support are positioned in the intervertebralspace. In specific embodiments, shock absorbing core locks into placewithin the upper plate or the lower plate.

In many embodiments, the core is positioned between the upper supportand the lower support when the upper support and the lower support areinserted into the intervertebral space. In specific embodiments, theupper support and the lower support articulate when the upper supportand the lower support are inserted into the intervertebral space.

In some embodiments, the shock absorbing core is compressed with aninstrument when the core is inserted into the intervertebral space. Theshock absorbing core can be compressed by at least about 0.5 mm when thecore is inserted into the intervertebral space.

In another aspect, an intervertebral disc prosthesis is provided. Theprosthesis comprises a resilient core. The core comprises an uppercomponent with an upper surface and a lower component with a lowersurface. At least one of a resilient material or a resilient member isdisposed between the upper and lower components so as to allow the upperand lower components to move resiliently toward and away from eachother. The upper and lower components define an inner chamber of thecore. At least one channel extends from the inner chamber to an externalsurface of the core to allow the passage of fluid through the chamber.The prosthesis also comprises upper and lower supports locatable aboutthe core. Each support comprises an outer surface which engages avertebra, and an inner surface shaped to contact one of the surfaces ofthe core. The upper and lower supports are adapted to articulate whenthe core is positioned between the upper and lower supports.

In some embodiments, the at least one channel comprises at least twochannels that extend from the chamber to the external surface of thecore to pass fluid through the core. the at least one channel can beadapted to pump fluid out of the core when the components move towardeach other and draw fluid into the core when the components move awayfrom each other.

In another aspect, an instrument for insertion of a intervertebral discprosthesis into an intervertebral space is provided. The instrumentcomprises a distractor tip that comprises a channel dimensioned to passthe prosthesis. The instrument also comprises at least one of aresilient member or a resilient material to compress the prosthesis froman expanded profile configuration to a narrow profile configuration withthe distractor tip when the prosthesis slides along the channel towardthe intervertebral space.

In many embodiments, a pair of handles is connected to the distractortip. The resilient member comprises a spring connected to the handles todrive the handles apart and compress the prosthesis to the narrowprofile configuration.

In another aspect, a system for insertion of an intervertebral discprosthesis into an intervertebral space is provided. The systemcomprises a plurality of selectable shock absorbing intervertebral discprosthesis cores, and an instrument. The instrument comprises adistractor tip with a channel dimensioned to pass the prosthesis. Thedistractor tip is capable of compressing at least one of the pluralityof cores from an expanded profile configuration to a narrow profileconfiguration when the prosthesis slides along the channel toward theintervertebral space.

In many embodiments, the expanded profile configuration comprises anunloaded configuration of the at least one of the plurality of cores,and the narrow profile configuration comprises a maximum loadedcompression of the at least one of the plurality of cores.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a cross-sectional anterior view of an intervertebral discprosthesis with the prosthesis plates and selected core in verticalalignment, according to embodiments of the present invention;

FIG. 1B is a side view of the prosthetic disc in FIG. 1 after slidingmovement of the plates over the selected core;

FIG. 1C is a cross-sectional view a the selected shock absorbing coresshown in detail, according to embodiments of the present invention;

FIG. 1D shows a plurality of selectable shock absorbing cores withdiffering heights and differing resiliencies, according to embodimentsof the present invention;

FIG. 1E schematically illustrates a first maximum angle of inclinationwith the first shock absorbing core of FIG. 1D positioned betweenendplates;

FIG. 1F schematically illustrates a second maximum angle of inclinationwith the second shock absorbing core of FIG. 1D positioned between theendplates;

FIG. 1G schematically illustrates a third maximum angle of inclinationwith the third shock absorbing core of FIG. 1D positioned between theendplates;

FIG. 1H shows a plurality of selectable shock absorbing cores withdiffering widths and differing resiliencies, according to embodiments ofthe present invention;

FIG. 2 is a cross-sectional view a prosthetic disc with a selected coreattached to a lower plate, according to embodiments of the presentinvention;

FIG. 3 shows an intervertebral prosthesis with an upper plate, a lowerplate, and a selected shock absorbing core that locks into the lowerplate to provide ball and socket motion, according to embodiments of thepresent invention;

FIGS. 4A-4E show a method of inserting a shock absorbing prosthesis,according to embodiments of the present invention;

FIG. 5 shows a shock absorbing core with channels to allow fluid to movethrough the core, according to embodiments of the present invention;

FIGS. 6A to 6D show a placement instrument 600 capable of compressingthe core when the implant is inserted into the intervertebral space,according to embodiments of the present invention; and

FIGS. 7A and 7B schematically illustrate details of the self-expandingintervertebral joint assembly loaded in a cartridge, in accordance withembodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Various embodiments of the present invention generally provide for anintervertebral disc prosthesis having upper and lower plates disposedabout a selectable core. The selectable core includes a resilientmaterial, which allows the core to absorb forces applied to it byvertebrae. The shock absorbing cores can be used with many prosthesisand approaches to the intervertebral disc space including anterior,lateral, posterior and posterior lateral approaches. Although variousembodiments of such a prosthesis are shown in the figures and describedfurther below, the general principles of these embodiments, namelyselecting a core with a force absorbing material in response to patientneeds, may be applied to any of a number of other disc prostheses, suchas but not limited to the LINK® SB Charite disc (provided by DePuySpine, Inc.) Mobidisk® (provided by LDR Medical (www.ldrmedical.fr)),the Bryan Cervical Disc and Maverick Lumbar Disc (provided by MedtronicSofamor Danek, Inc.), the ProDisc® or ProDisc-C® (from Synthes Stratec,Inc.), and the PCM disc (provided by Cervitech, Inc.). In someembodiments, the selectable core can be used with an expandableintervertebral prosthesis, as described in U.S. application Ser. No.11/787,110, entitled “Posterior Spinal Device and Method”, filed Apr.12, 2007, the full disclosure of which is incorporated herein byreference.

FIGS. 1A to 1C show a prosthetic disc 10 comprising a selected shockabsorbing core, according to embodiments of the present invention. Disc10 for intervertebral insertion between two adjacent spinal vertebrae(not shown) suitably includes an upper plate 12, a lower plate 14 and aselected shock absorbing core 16 located between the plates. The upperplate 12 includes an outer surface 18 and an inner surface 24 and may beconstructed from any suitable metal, alloy or combination of metals oralloys, such as but not limited to cobalt chrome molybdenum, titanium(such as grade 5 titanium), stainless steel and/or the like. In oneembodiment, typically used in the lumbar spine, the upper plate 12 isconstructed of cobalt chrome molybdenum, and the outer surface 18 istreated with aluminum oxide blasting followed by a titanium plasmaspray. In another embodiment, typically used in the cervical spine, theupper plate 12 is constructed of titanium, the inner surface 24 iscoated with titanium nitride, and the outer surface 18 is treated withaluminum oxide blasting. An alternative cervical spine embodimentincludes no coating on the inner surface 24. In other cervical andlumbar disc embodiments, any other suitable metals or combinations ofmetals may be used. In some embodiments, it may be useful to couple twomaterials together to form the inner surface 24 and the outer surface18. For example, the upper plate 12 may be made of an MRI-compatiblematerial, such as titanium, but may include a harder material, such ascobalt chrome molybdenum, for the inner surface 24. In anotherembodiment, upper plated 12 may comprise a metal, and inner surface 24may comprise a ceramic material. All combinations of materials arecontemplated within the scope of the present invention. Any suitabletechnique may be used to couple materials together, such as snapfitting, slip fitting, lamination, interference fitting, use ofadhesives, welding and/or the like. Any other suitable combination ofmaterials and coatings may be employed in various embodiments of theinvention.

In some embodiments, the outer surface 18 is planar. Oftentimes, theouter surface 18 will include one or more surface features and/ormaterials to enhance attachment of the prosthesis 10 to vertebral bone.For example, the outer surface 18 may be machined to have serrations 20or other surface features for promoting adhesion of the upper plate 12to a vertebra. In the embodiment shown, the serrations 20 extend inmutually orthogonal directions, but other geometries would also beuseful. Additionally, the outer surface 18 may be provided with a roughmicrofinish formed by blasting with aluminum oxide microparticles or thelike. In some embodiments, the outer surface may also be titanium plasmasprayed to further enhance attachment of the outer surface 18 tovertebral bone.

The outer surface 18 may also carry an upstanding, vertical fin 22extending in an anterior-posterior direction. The fin 22 is pierced bytransverse holes 23. In alternative embodiments, the fin 22 may berotated away from the anterior-posterior axis, such as in alateral-lateral orientation, a posterolateral-anterolateral orientation,or the like. In some embodiments, the fin 22 may extend from the surface18 at an angle other than 90.degree. Furthermore, multiple fins 22 maybe attached to the surface 18 and/or the fin 22 may have any othersuitable configuration, in various embodiments. In some embodiments,such as discs 10 for cervical insertion, the fins 22, 42 may be omittedaltogether.

The inner, spherically curved concave surface 24 is formed at a central(from right to left), axial position with a circular recess 26 asillustrated. At the outer edge of the curved surface 24, the upper plate12 carries peripheral restraining structure comprising an integral ringstructure 26 including an inwardly directed rib or flange 28. The flange28 forms part of a U-shaped member 30 joined to the major part of theplate by an annular web 32. The flange 28 has an inwardly tapering shapeand defines upper and lower surfaces 34 and 36 respectively which areinclined slightly relative to the horizontal when the upper plate 12 isat the orientation seen in FIG. 1. An overhang 38 of the U-shaped member30 has a vertical dimension that tapers inwardly as illustrated.

The lower plate 14 is similar to the upper plate 12 except for theabsence of the peripheral restraining structure 26. Thus, the lowerplate 14 has an outer surface 40 which is planar, serrated andmicrofinished like the outer surface 18 of the upper plate 12. The lowerplate 14 optionally carries a fin 42 similar to the fin 22 of the upperplate. The inner surface 44 of the lower plate 14 is concavely,spherically curved with a radius of curvature matching that of the innersurface 24 of the upper plate 12. Once again, this surface may beprovided with a titanium nitride or other finish.

At the outer edge of the inner curved surface 44, the lower plate 14 isprovided with an inclined ledge formation 46. Alternatively, the lowerplate 14 may include peripheral restraining structure analogous to theperipheral restraining structure 26 on the upper plate 12.

The selected shock absorbing core 16 is symmetrical about a central,equatorial plane 52 which bisects it laterally. (Although in otherembodiments, the selected shock absorbing core 16 may be asymmetrical.)Lying on this equatorial plane is an annular recess or groove 54 whichextends about the periphery of the selected shock absorbing core. Thegroove 54 is defined between upper and lower ribs or lips 56. When theplates 12, 14 and selected shock absorbing core 16 are assembled and inthe orientation seen in FIG. 1, the flange 28 lies on the equatorialplane and directly aligned with the groove 54. The outer diameter 58 ofthe lips 56 is preferably very slightly larger than the diameter 60defined by the inner edge of the flange 28. In some embodiments, theselected shock absorbing core 16 is movably fitted into the upper plate12 via an interference fit. To form such an interference fit with ametal component of selected core 16 and metal plate 12, any suitabletechniques may be used. For example, the plate 12 may be heated so thatit expands, and the component of selected core 16 may be dropped intothe plate 12 in the expanded state. When the plate 12 cools andcontracts, the interference fit is created. In another embodiment, theupper plate 12 may be formed around the component of selected shockabsorbing core 16. Alternatively, the selected shock absorbing core 16and upper plate 12 may include complementary threads, which allow theselected shock absorbing core 16 to be screwed into the upper plate 12,where it can then freely move.

The central axis of the disc 10 (the axis passing through the centers ofcurvature of the curved surfaces) is indicated with the referencenumeral 62. As shown in FIG. 1, the disc 10 may be symmetrical about acentral anterior-posterior plane containing the axis 62. In someembodiments the axis 62 is posteriorly disposed, i.e. is located closerto the posterior limit of the disc than the anterior limit thereof.

In use, the disc 10 is surgically implanted between adjacent spinalvertebrae in place of a damaged disc. The adjacent vertebrae areforcibly separated from one another to provide the necessary space forinsertion. The disc 10 is typically, though not necessarily, advancedtoward the disc space from an anterolateral or anterior approach and isinserted in a posterior direction—i.e., from anterior to posterior. Thedisc is inserted into place between the vertebrae with the fins 22, 42of the plates 12, 14 entering slots cut in the opposing vertebralsurfaces to receive them. During and/or after insertion, the vertebrae,facets, adjacent ligaments and soft tissues are allowed to move togetherto hold the disc in place. The serrated and microfinished surfaces 18,40 of the plates 12, 14 locate against the opposing vertebrae. Theserrations 20 and fins 22, 42 provide initial stability and fixation forthe disc 10. With passage of time, enhanced by the titanium surfacecoating, firm connection between the plates and the vertebrae will beachieved as bone tissue grows over the serrated surface. Bone tissuegrowth will also take place about the fins 22, 40 and through thetransverse holes 23 therein, further enhancing the connection which isachieved.

In the assembled disc 10, the complementary and cooperating sphericalsurfaces of the plates and selected shock absorbing core allow theplates to slide or articulate over the selected core through a fairlylarge range of angles and in all directions or degrees of freedom,including rotation about the central axis 62. FIG. 1A shows the disc 10with the plates 12 and 14 and selected shock absorbing core 16 alignedvertically with one another on the axis 62. FIG. 1B illustrates asituation where maximum anterior flexion of the disc 10 has taken place.At this position, the upper rib 56 has entered the hollow 38 of theU-shaped member 30, the lower surface of the rib 56 has moved intocontact with the upper surface 34 of the flange 28, the flange havingmoved into the groove 54, and the lower surface 36 of the flange hasmoved into contact with the upper surface of the ledge formation 46, aswill be seen in the encircled areas 69. Abutment between the varioussurfaces prevents further anterior flexure. The design also allows forthe inner extremity of the flange 28 to abut against the base of thegroove 54, thereby limiting further relative movement between theselected core and plate. A similar configuration is achieved in theevent of maximum posterior flexure of the plates 12, 14 over theselected shock absorbing core, such as during spinal extension and/or inthe event of maximum lateral flexure.

The flange 28 and the groove 54 defined between the ribs 56, preventseparation of the selected core from the plates. In other words, thecooperation of the retaining formations ensures that the selected shockabsorbing core is held captive between the plates at all times duringflexure of the disc 10.

In an alternative embodiment, the continuous annular flange 28 may bereplaced by a retaining formation comprising a number of flange segmentswhich are spaced apart circumferentially. Such an embodiment couldinclude a single, continuous groove 54 as in the illustrated embodiment.Alternatively, a corresponding number of groove-like recesses spacedapart around the periphery of the selected core could be used, with eachflange segment opposing one of the recesses. In another embodiment, thecontinuous flange or the plurality of flange segments could be replacedby inwardly directed pegs or pins carried by the upper plate 12. Thisembodiment could include a single, continuous groove 54 or a series ofcircumferentially spaced recesses with each pin or peg opposing arecess.

In yet another embodiment, the retaining formation(s) can be carried bythe lower plate 14 instead of the upper plate, i.e. the plates arereversed. In some embodiments, the upper (or lower) plate is formed withan inwardly facing groove, or circumferentially spaced groove segments,at the edge of its inner, curved surface, and the outer periphery of theselected core is formed with an outwardly facing flange or withcircumferentially spaced flange segments.

Referring now to FIG. 1C, a cross-sectional view of a selected shockabsorbing core 16 is shown in detail. Core 16 comprises an uppercomponent 70 and a lower component 72. Upper component 70 and lowercomponent 72 define a chamber 71. A resilient material 74 can bepositioned between upper component 70 and lower component 72 withinchamber 71. Resilient material 74 may extend between from one componentto the other to component, such that upper component 70 is supportedwith the resilient material. Resilient material 74 may comprise manyknown resilient materials, for example an elastomer such as siloxane. Atleast one resilient member can be positioned between upper component 70and lower component 72. The at least one resilient member may comprisemany known resilient members, for example a spring 76A, a spring 76B anda spring 76C. In some embodiments, resilient member 74 is positionedbetween the upper and lower components to provide shock absorptionwithout the springs. In some embodiments, the at least one resilientmember is positioned between the upper and lower components without theresilient material. The resilient materials and at least one resilientmember may comprise resilient materials and members as described in U.S.application Ser. No. 11/051,513, entitled “Intervertebral ProstheticDisc with Shock Absorption”, filed on Feb. 4, 2005, the full disclosureof which is incorporated herein by reference.

Upper component 70 and lower component 72 are configured to sliderelative to one another. Upper component 70 comprises an upper slidestructure, for example an inner annular sleeve 82. Lower component 72comprises a lower slide structure, for example an outer annular sleeve84. The upper slide structure mates with the lower slide structure, suchthat the two slide structures permit the upper component to sliderelative to the lower component, for example with a telescopic slidemechanism 80.

In some embodiments, the sequential motion of the core parts relative toeach other can change the volume chamber 71 so as to provide an inflowand outflow of bodily fluids between the sliding members of the core,such that the fluid flow provides and facilitates lubrication of thesliding members with bodily fluids.

When implanted between vertebrae, at least one of resilient material 74or the at least one resilient member can resiliently absorb shockstransmitted vertically between upper and lower vertebrae of thepatient's spinal column. This shock absorption is related to thematerial properties and dimensions of the resilient material andresilient members, for example Young's modulus of elasticity. Ingeneral, an increased thickness of the resilient material and/or memberswill increase absorbance of shocks, with more elastic, or springycompression between the vertebrae. In some embodiments, the resilientmaterial may comprise a damping material and/or damping characteristicsto improve shock absorption. For example, many resilient materials asdescribed herein also comprise damping materials.

Selected shock absorbing core 16 comprises a height 78 and a width 58that can be related to the shock absorbing characteristics of the coreand/or prosthesis. In many embodiments, the core can absorb shocks tothe vertebrae with compression along height 78, such that height 78 candecrease with compression of the core due to forces along the spine. Asthe thickness of the prosthesis is related to the height of the core, insome embodiments the height of the prosthesis will change with the core,for example decrease when the core is compressed. In many embodiments,the height of the prosthesis corresponds to a distance between serratedand microfinished surfaces 18, 40 of the plates 12, 14 that locateagainst the opposing vertebrae. In some embodiments, an increase ofheight 78 can increase shock absorption and resiliency of the core, forexample with increased thickness of the shock absorbing materials and/orincreased length of the resilient members, for example the resilientmembers such as compressible resilient springs. In some embodiments,width 58 of the selected core may also affect properties of theendplates.

Referring now to FIG. 1D, a plurality 100 of selectable shock absorbingcores is shown with differing heights and differing resiliencies,according to embodiments of the present invention. Plurality 100comprises a first core 110A, a second core 110B and a third core 110C.

First core 110A comprises an upper component 116A and a lower component118A. A resilient material 112A is disposed between upper component 116Aand lower component 118A. At least one resilient member 114A extendsbetween upper component 116A and lower component 118A. First core 110Acomprises a first height 122A. Resilient material 112A comprises athickness 124A that corresponds to a length of at least one resilientmember 114A. The resilience and shock absorption of first core 110Acorresponds to thickness 124A, such that the resilience and shockabsorption increase with increasing of thickness of 124A. First core110A comprises an indicia, for example a marking 120A on the lowercomponent to identify the first core, such that first core 110A can beidentified and selected from among plurality 100.

Second core 110B comprises an upper component 116B and a lower component118B. A resilient material 112B is disposed between upper component 116Band lower component 118B. At least one resilient member 114B extendsbetween upper component 116B and lower component 118B. Second core 110Bcomprises a second height 122B. Resilient material 112B comprises athickness 124B that corresponds to a length of at least one resilientmember 114B. The resilience and shock absorption of second core 110Bcorresponds to thickness 124B, such that the resilience and shockabsorption increase with increasing of thickness of 124B. Second core110B comprises an indicia, for example a marking 120B on the lowercomponent to identify the second core, such that second core 110B can beidentified and selected from among plurality 100.

Third core 110C comprises an upper component 116C and a lower component118C. A resilient material 112C is disposed between upper component 116Cand lower component 118C. At least one resilient member 114C extendsbetween upper component 116C and lower component 118C. Third core 110Ccomprises a third height 122C. Resilient material 112C comprises athickness 124C that corresponds to a length of at least one resilientmember 114C. The resilience and shock absorption of third core 110Ccorresponds to thickness 124C, such that the resilience and shockabsorption increase with increasing thickness of 124C. Third core 110Ccomprises an indicia, for example a marking 120C on the lower componentto identify the third core, such that third core 110C can be identifiedand selected from among plurality 100.

In many embodiments, some characteristics first core 110A, second core110B and third core 110C are substantially the same, such that the coresare interchangeable. For example, a radius of curvature of the uppercomponent of each core may be substantially the same, such that theplates articulate without point contact between the upper curve surfaceof the upper components. Resilient material 112A, resilient material112B and resilient material 112C may comprise the substantially the sameresilient material, for example an elastomer. In some embodiments, thecurved surfaces of the lower components of each core may besubstantially the same such that the selected core can slide over thebottom endplate.

In many embodiments, the cores may comprise predeterminedcharacteristics that can be identified by the markings For example,third core 110C may comprise the most resilient core of the pluralitywith the most shock absorption, while first core 110A may comprise theleast resilient core of the plurality with the least shock absorption.Also, third core 110C may comprise the core which provides the largestmaximum angle of inclination between the plates of the plurality, whilefirst core 110A may comprise core which provides the smallest angle ofinclination between the plates.

In many embodiments, each core of the plurality of core comprises anintended maximum compression under normal patient activity. In someembodiments, first core 110A comprises a maximum compression of ⅓ mmalong first height 122A with normal patient activity; second core 110Bcomprises a maximum compression of ⅔ mm along second height 122B withnormal patient activity; and third core 110C comprises a maximumcompression of 1 mm along third height 122C with normal patientactivity. In some embodiments, the maximum compression can be limitedwith stops, for example maximum travel of inner sleeve 82 relative toouter sleeve 84 such that inner sleeve 82 on upper component 70 contactslower core component 72 to limit compression. In some embodiments, theplurality of cores may comprise a substantially incompressible core, forexample a core made entirely of metal, such as cobalt chrome. In suchembodiments, the range of compression provided by the plurality of corescan be from about 0 mm to about 1 mm. A core with maximum compression ofsubstantially zero may comprises a core made entirely from metal, forexample cobalt chrome.

FIG. 1E schematically illustrates a first maximum angle of inclination108A with the first shock absorbing core of FIG. 1D positioned betweenan upper endplate 102 and a lower endplate 104. First shock absorbingcore 110A comprises first thickness 122A. At maximum angle ofinclination 108A, upper plate 102 contacts lower plate 104 at a contactlocus 106, for example contact formations as described above. Maximumangle of inclination 108A is determined by thickness 122A.

FIG. 1F schematically illustrates a second maximum angle of inclination108B with the second shock absorbing core of FIG. 1D positioned betweenupper endplate 102 and lower endplate 104. Second shock absorbing core110B comprises second thickness 122B. At maximum angle of inclination108B, upper plate 102 contacts lower plate 104 at contact locus 106, forexample contact formations as described above. Maximum angle ofinclination 108B is determined by thickness 122B.

FIG. 1G schematically illustrates a third maximum angle of inclination108C with the third shock absorbing core of FIG. 1D positioned betweenupper endplate 102 and lower endplate 104. Third shock absorbing core110C comprises third thickness 122C. At maximum angle of inclination108C, upper plate 102 contacts lower plate 104 at contact locus 106, forexample contact formations as described above. Maximum angle ofinclination 108C is determined by thickness 122C.

In some embodiments, the plurality of cores may comprise a constantheight among the cores such that the maximum angle of inclinationremains constant, while the shock absorption varies. In suchembodiments, the thickness of the resilient material and/or thickness ofthe at least one resilient member differ among the cores of theplurality, while thicknesses of the upper and lower components differ soas to compensate for the different thicknesses of the resilient materialand/or thickness of the at least one resilient member. Thus, thethicknesses of the cores among the plurality remain constant.

Referring now FIG. 1H a plurality 140 of selectable shock absorbingcores of constant height is shown with differing widths and differingresiliencies. Plurality 140 comprises a first core 150A, a second core150B and a third core 150C.

First core 150A comprises an upper component 156A and a lower component158A. A resilient material 152A is disposed between upper component 156Aand lower component 158A. At least one resilient member 154A extendsbetween upper component 156A and lower component 158A. First core 150Acomprises a first height 162A and a first dimension across 166A, forexample a diameter. Resilient material 152A comprises a thickness 164Athat corresponds to a length of at least one resilient member 154A. Theresilience and shock absorption of first core 160A corresponds tothickness 164A, such that the resilience and shock absorption increasewith increasing of thickness 164A. First core 150A comprises an indicia,for example a marking 160A on the lower component to identify the firstcore, such that first core 150A can be identified and selected fromamong plurality 140.

Second core 150B comprises an upper component 156B and a lower component158B. A resilient material 152B is disposed between upper component 156Band lower component 158B. At least one resilient member 154B extendsbetween upper component 156B and lower component 158B. Second core 150Bcomprises a second height 162B and a second dimension across 166B, forexample a diameter. Resilient material 152B comprises a thickness 164Bthat corresponds to a length of at least one resilient member 154B. Theresilience and shock absorption of second core 160B corresponds tothickness 164B, such that the resilience and shock absorption increasewith increasing of thickness 164B. Second core 150B comprises anindicia, for example a marking 160B on the lower component to identifythe second core, such that second core 150B can be identified andselected from among plurality 140.

Third core 150C comprises an upper component 156C and a lower component158C. A resilient material 152C is disposed between upper component 156Cand lower component 158C. At least one resilient member 154C extendsbetween upper component 156C and lower component 158C. Third core 150Ccomprises a third height 162C and a third dimension across 166C, forexample a diameter. Resilient material 152C comprises a thickness 164Cthat corresponds to a length of at least one resilient member 154C. Theresilience and shock absorption of third core 160C corresponds tothickness 164C, such that the resilience and shock absorption increasewith increasing of thickness 164C. Third core 150C comprises an indicia,for example a marking 160C on the lower component to identify the secondcore, such that third core 150C can be identified and selected fromamong plurality 140.

The height of several cores of the plurality is substantially the same,such that the maximum angle of inclination between the plates issubstantially the same for each of the several cores. In someembodiments, first height 162A, second height 162B and third height 162Care substantially the same, such that the maximum angle of inclinationof the plates is substantially the same.

The each core of the plurality can be identified in many ways. In someembodiments, the core may comprise an indicia that comprises at leastone of a color of the core, a marking on the core, a height of the coreor a width of the core. The indicia may be located on the uppercomponent of the core, or the lower component of the core.

The resilient material may comprise many known materials and maycomprise at least one resilient material. In some embodiments, the atleast one resilient material comprises a polymer. The at least oneresilient material may comprise a hydrogel. The at least one resilientsupport member may be disposed within the resilient material andattached to the upper and lower components comprising the upper andlower curved surfaces.

In many embodiments, the upper and lower components and the curvedsurfaces formed thereon comprise at least one a polymer, a ceramic or ametal. The metal can comprise at least one of cobalt chrome molybdenum,titanium or stainless steel.

Referring now FIG. 2, a cross-sectional view is shown of a prostheticdisc 200 with a selected shock absorbing core 230 attached to a lowerplate 220. Selected shock absorbing core can be selected from aplurality of cores, for example as described above. Prosthetic disc 200comprises an upper plate 210. Selected shock absorbing core 230 ispositioned between the upper plate and the lower plate. Selected shockabsorbing core 230 comprises a lower component 232 and an uppercomponent 234. Core 230 comprises a resilient material between uppercomponent 234 and lower component 232. At least one resilient member,for example coils 238 is shown between upper component 234 and lowercomponent 232. Lower component 232 comprises a lower slide structure233, for example an annular inner sleeve. Upper component 234 comprisesan upper slide structure, for example an outer annular sleeve 235. Theupper and slide structures comprise a sliding structure, for example asliding telescopic joint, such that the selected core and resilientlyabsorb shocks to the prosthesis when positioned in the intervertebralspace.

Lower plate 220 can be attached to selected shock absorbing core 230 inmany known ways. For example, the selected shock absorbing core can beattached to lower plate by locking the selected core into the lowerplate with a detent. Lower plate 220 comprises threads 222 to attach theselected shock absorbing core to the lower plate, for example in theoperating room before the prosthesis is inserted into the intervertebralspace.

In some embodiments, the shock absorbing core can be inserted betweenthe intervertebral plates after the plates have been inverted into theintervertebral space, as described in U.S. Pat. No. 6,936,071, the fulldisclosure of which is incorporated herein by reference. The core can becompressed to a low profile configuration when the core is insertedbetween the plates to minimize distraction of the vertebrae when thecore is inserted between the plates. Once the core is locked intoposition, the core can provide two piece ball and socket motion andshock absorption.

Shock absorbing core 230 comprises and an upper curved spherical surface235. Upper plate 210 comprises a lower curved spherical surface 212.Upper curved spherical surface 235 and lower curved spherical surface212 each comprises a radius of curvature. The radius of curvature of theupper curved spherical surface 235 and lower curved spherical surface212 are substantially the same, such that the upper and lower curvedsurfaces form a ball and socket joint, as described in U.S. Pat. No.6,740,118, the full disclosure of which is incorporated by reference. Insome embodiments, the selected shock absorbing core comprises andindicia to identify the core, for example a letter etched in uppercurved spherical surface 235.

FIG. 3 shows an intervertebral prosthesis 300 with an upper plate 310, alower plate 320, and a selected shock absorbing core 330 that locks intothe lower plate to provide ball and socket motion. Selected shockabsorbing core 330 comprises a core selected from a plurality of shockabsorbing cores as described above. Upper plate 310 comprises a channel312 and a channel 314, for example as described in U.S. Pat. No.6,936,071, the full disclosure of which is incorporated by reference.Lower plate 320 comprises a channel 322 sized to receive core 330. Lowerplate 320 comprises a channel 324, and an indentation 326. Lower plate320 may comprise a second channel similar to channel 324 that isdisposed on the lower plate equidistant from the middling of the lowerplate and opposite the midline. Selected shock absorbing core 330comprises a flange 334 and a detent 332.

The upper plate 310 and lower plate 320 are sized to nest together wheninserted into the intervertebral space, as indicated by lines 340. Oncethe upper and lower plates are positioned together in the intervertebralspace, selected shock absorbing core 330 can be slid between upper plate310 and lower plate 320 as indicated by lines 350. Channel 322 receivesthe selected shock absorbing core and flange 334. When the selectedshock absorbing core is positioned in the lower plate, detent 332extends into indentation 326 so as to lock the selected shock absorbingcore into position in lower plate 320.

Channel 312, channel 314 and channel 324 are sized to receive prongs ofan insertion tool, for example as describe in U.S. Pat. No. 5,314,477,the full disclosure of which is incorporated herein by reference. Insome embodiments, the channels on the upper and lower plate receive aninstrument that presses the upper and lower plates together so as tocompress core 330 and minimize distraction when the core is insertedbetween the upper and lower plates while the plates are position in theintervertebral space.

Referring now to FIGS. 4A-4E a method is shown for inserting anintervertebral disc prosthesis 404 comprising a selected shock absorbingshock absorbing core 412, according to embodiments of the presentinvention. Prosthesis 402 is inserted into an intervertebral space ISbetween two adjacent vertebrae V with a resilient shock absorbing corethat can compress during insertion into the disc space so as to minimizedistraction. The method involves selecting a shock absorbing core, asdescribed above, and inserting the disc prosthesis 404 partway into thespace IS while the prosthesis 404 is constrained (FIG. 4A), for exampleas described in U.S. application Ser. No. 10/913,780, entitled “Methodsand Apparatus for Invertebral Disc Prosthesis Insertion”, the fulldisclosure of which is incorporated herein by reference. To insert theprosthesis 404 partway under constraint, an insertion device 402 may beused. Such an insertion device 402 may suitably include a graspingmember 410 coupled with an elongate shaft 408. At an end opposite thegrasping member 410 (not shown), the insertion device 402 may include ahandle, an actuator to control the grasping member 410 and/or any othersuitable features.

The prosthesis 404 may be inserted as far into the intervertebral spaceIS under constraint as is desired. In some embodiments, for example, theprosthesis 404 is inserted under constraint approximately one-third ofthe way into the space IS. In other embodiments, the prosthesis 404 maybe inserted less than one-third of the way, closer to one-half of theway, or any other suitable distance into the space IS.

As shown in FIG. 4B, once the prosthesis 404 is inserted partway underconstraint, the insertion device 402 may be removed, thus releasing theprosthesis 404 from constraint. From this point forward, the endplates406 of the prosthesis 404 are free to move about the prosthesis shockabsorbing core 412. Examples of such a prosthesis 404 with endplates 406and selected shock absorbing core 412 are described above.

Referring now to FIGS. 4C-4E, in some embodiments the insertion device402 may be used to push the unconstrained prosthesis 404 farther intothe intervertebral space. In some embodiments, one or more separatepusher devices may be used in addition to or instead of the insertiondevice 402 for pushing the prosthesis 104 farther into the space IS.FIGS. 4C and 4D show that the grasping member 410 of the insertiondevice 402 can be adapted to push individually against the upper (FIG.4C) and lower (FIG. 4D) endplates 406. As shown in FIG. 4E, the graspingmember 410 may also be adapted to push simultaneously against the upperand lower endplates 406, thus pushing the prosthesis 404 as a unitfarther into the intervertebral space IS.

By inserting the prosthesis 404 farther into the space IS while it isunconstrained and compressing the shock absorbing core, thus allowingthe endplates 406 to articulate about the shock absorbing core 412 andcome closer together, the method reduces the need for increasing theheight of the intervertebral space IS with distraction of the vertebraeV away from each other. Because the endplates 406 are free to articulateand can compress the shock absorbing core 416 to move the platestogether, the prosthesis 404 is better able to conform to theintervertebral space IS, thus reducing trauma to the vertebrae V andalso limiting trauma to surrounding structures caused byover-distraction.

The unconstrained prosthesis 404 may be inserted as far into theintervertebral space IS as is desired. In some embodiments, for example,the prosthesis 404 is pushed far enough into the space IS so that acenter of rotation of the prosthesis 404 is closer to a posterior edge P(FIG. 4E) of the vertebrae V than to an anterior edge A of the vertebraeV. In alternative embodiments, any other suitable insertion distance ordepth may be used. Once a desired amount of insertion is achieved, theinsertion device 402 is removed and the prosthesis 404 is in placebetween the two adjacent vertebrae V.

In various embodiments, the method just described may include fewersteps or additional steps. For example, in one embodiment, a spreaderdevice is inserted between the two vertebrae V to spread them apartbefore inserting the constrained prosthesis 404. An example of such aspacing device is described in PCT Patent Application No. 2004/000171,the full disclosure of which is incorporated by reference. In suchembodiments, the insertion device 402 can be sized to fit betweenopposing jaws of the spreader device, such that the jaws can compressthe shock absorbing core so as to minimize distraction. When theprosthesis 404 is partially inserted, the spreader device is removedfrom the intervertebral space IS, and the prosthesis 404 is releasedfrom constraint and inserted the rest of the way into the space IS. Alsoin some embodiments, a midline indicator device may be used tofacilitate the location of a midline on one or both of the two adjacentvertebrae V. An example of such a midline indicator device is describedin PCT Patent Application No. 2004/000170, the full disclosure of whichis incorporated herein by reference. In some embodiments, the midlineindicator can be used before the disc prosthesis 404 is inserted. Theseand other steps or features may be included in various embodiments ofthe method without departing from the scope of the invention.

FIG. 5 shows a shock absorbing core 500 with channels to allow fluid tomove through the core, according to embodiments of the presentinvention. Many components of core 500 are similar to core 16 shownabove. Core 500 comprises a channel 510, a channel 512, a channel 514and a channel 516. An upper component 570 and lower component 572 ofcore 500 define a chamber 502. Resilient material 574 and resilientmember 76A, resilient member 76B and resilient member 76C can bedisposed between the upper and lower components within chamber 502.Resilient material 574 may comprise an upper channel 520 and a lowerchannel 522 to permit drainage from resilient material 574 and/or thechamber. In many, embodiments, core 500 comprises channel 510, channel512, channel 514 and channel 516 without resilient material 574. Channel510, channel 512, channel 514 and channel 516 extend from chamber 502 toan external surface of core 500 to permit fluid to drain from the coreand/or pass through the core.

The channels in the upper and lower components and resilient material incore 500 permit fluid to pass through the core while the patient isstationary and can pump fluid through the core during patient activity.Work in relation to embodiments of the present invention suggests thatstatic accumulation of bodily fluids in the core may occur. By passingfluid through the core, bacteria build up due to static enclosed fluidsmay be avoided. When upper component 570 moves toward lower component572 a volume of chamber 502 decreases so as to drive fluid, for examplebodily fluid from chamber 502. When the upper component 520 moves awayfrom lower component 572, the volume of chamber 502 increases so as todraw fluid into the chamber. As an active person will resilientlycompress and expand core 500 with activity, core 500 can pump fluid inand out of the core by moving the upper and lower components toward andaway from each other with patient movement. In many embodiments, thechannels are large enough to enable fluid flow, and small enough toinhibit tissue in growth that may compromise the shock absorbing motionof the core. The number of channels in the upper and lower componentsand/or resilient material can be selected so as to enable fluid flow andnot weaken the core structures.

FIGS. 6A to 6D show a placement instrument 600 capable of compressingthe core when the implant is inserted into the intervertebral space,according to embodiments of the present invention. The placementinstrument can be inserted posteriorly through the canal and/or foramenso as to engage the boney endplates near the disc space, as described inU.S. application Ser. No. 11/787,110, entitled “Posterior Spinal Deviceand Method”, filed Apr. 12, 2007, the full disclosure of which haspreviously been incorporated herein by reference. In many embodiments,the placement instrument is inserted after two minimally invasive Wiltseincisions and/or dissections and a discectomy that uses a posteriorparallel distractor. Placement instrument 600 comprises a distractorwith a distractor tip 630 that can be inserted at least partially intothe intervertebral space. Instrument 600 comprises a stop to limitpenetration of distractor tip 630. Instrument 600 comprises handles 610to distract the adjacent vertebrae. Instrument 600 comprises a hinge 620that opens distractor tip 630 upon inward motion of handles 610.

Instrument 600 comprises a compression spring 615 that presses handles610 apart, so as to oppose inward motion of the handles. By forcinghandles 610 apart, compression spring 615 can close distractor tip 630so as to compress the core to a narrow profile configuration.

Instrument 600 is adapted to pass the prostheses in an elongate narrowprofile configuration into the intervertebral space. Distractor tip 630comprises a channel 640 with grooves 642 formed therein. Channel 640 isdimensioned to pass the prosthesis in an elongate narrow profileconfiguration. Grooves 642 are dimensioned and spaced to receive anchorson the external surfaces of the support components, for examplepyramidal components as described above. In some embodiments, theanchors may comprise elongate pyramidal anchors and or elongate keels orflanges and the grooves adapted to pass the elongate anchors with thegroove aligned with the elongate anchor. In many embodiments, channel640 is sized to distract the vertebrae with distractor tip 630 while theelongate prosthesis slides down channel 640. Near hinge 620, channel 640can be sized to pass the prosthesis with a sliding fit.

Instrument 600 comprises an insertion tool 650 to advance the prosthesisalong channel 640 so as to advance the prosthesis into theintervertebral space. Insertion tool 650 comprises a shaft 654 and ahandle 652. Handle 652 is connected to shaft 654. In many embodimentshandle 652 comprises a grub screw, and handle 652 and shaft 654 comprisestrong materials such that handle 652 can be hammered so as to drive theprosthesis distally into the intervertebral space and distract thevertebrae with separation of distal tip 630. Compression spring 1651 canexpand to force handles 610 open and close distractor tip 630 so as topress the upper and lower supports of the prosthesis together andcompress the selected shock absorbing core. This compression of theshock absorbing core can reduce the height of the prosthesis and reducedistraction of the intervertebral space and/or surrounding tissues whenthe implant is inserted into the intervertebral space.

The selectable shock absorbing cores and insertion tool may comprise asystem for narrow profile insertion of the prosthesis into theintervertebral space so as to minimize distraction. The compressionspring can compress the shock absorbing prosthesis to a narrow profileconfiguration. Although a compression spring is shown, many springsand/or resilient members and/or materials can be used to compress theprosthesis to a narrow profile configuration, for example resilientmaterials and members similar to those used in the core as describedabove. In many embodiments, the selected core provides maximumcompression within a range from about ⅓ mm to about 1 mm during patientactivity, and the narrow profile configuration of the core comprises amaximum compression of the core, for example ⅓ mm, ⅔ mm or 1 mm,depending on the core as described above. In many embodiments, anexpanded configuration of the core comprises an unloaded configurationof the core. In many embodiments, the resilient member and/or materialis connected to the distractor tips so as to compress the selected shockabsorbing prosthesis and/or core to the narrow profile configuration,for example with maximum compression of the core as described above,when the core is positioned in the channel for insertion into thepatient.

FIGS. 7A and 7B schematically illustrate a selectable shock absorbingcore and details of a self-expanding intervertebral joint assemblyloaded in a cartridge as described in U.S. application Ser. No.11/787,110, entitled “Posterior Spinal Device and Method”, filed Apr.12, 2007, the full disclosure of which has previously been incorporatedherein by reference. A system comprising shock absorbing cores, asdescribed above, can be provided to the physician. The physician canselect the core from among a plurality of cores as described above.

Outer cartridge casing 820 extends over at least a portion ofintervertebral joint assembly to permit advancement of the jointassembly into at least a portion of the intervertebral space while thejoint assembly is substantially covered with outer cartridge casing 820.Outer cartridge casing 820 covers pyramidal anchors 712 and pyramidalanchors 714. Distal component 720 of upper support 702 and distalcomponent 730 of lower support 704 are located near an opening in outercartridge casing 820. Inner cartridge part 830 includes a wedge 832,upper flange 836 and lower flange 838. The upper and lower flangesinclude inner opposing surfaces, and the inner surface of each flangeopposes one of the wedge surfaces to clamp the components of the upperand lower supports in a parallel configuration Inner cartridge part 830is connected to shaft 840.

Self expanding intervertebral joint assembly 700 includes structures topermit articulation between upper support 702 and lower support 704 torestore motion between the vertebrae. Upper support 702 has a protrudingstructure 725 which extends from middle component 724 and has a concavesurface feature formed therein, as shown herein above, which mates theupper surface of shock absorbing biconvex core 706. Lower support 704has a protruding structure 735 which extends from middle component 734and has a concave surface feature formed therein, which mates the lowersurface of shock absorbing biconvex core 706. In an alternateembodiment, the features of the upper and lower support are in directcontact and mate to provide articulation. For example, the upper supportcan have a protrusion with a convex surface, and the lower support canhave a protrusion with a concave surface, in which the two surfaces mateto form a load bearing articulate joint.

Protruding structure 725 and protruding structure 726 can also includestructures to retain the shock absorbing biconvex core and upper andlower retention ring gears, respectively. In many embodiments, shockabsorbing core 607 comprises an annular channel 707 around the peripheryof the shock absorbing core Annular channel 707 is sized to receiveretention ring structures of the upper and lower plates, so as to retainthe shock absorbing core between the plates.

Protruding structure 725 can include a retention ring, rim or annularflange as described above such as an annular flange 770 that projectsradially inward toward shock absorbing biconvex core 706 to retain shockabsorbing biconvex core 706. Protruding structure 735 can include aradially inwardly projecting retention ring, rim or annular flange suchas an annular flange 771 that extends toward shock absorbing biconvexcore 706 to retain shock absorbing biconvex core 706. Annular flange 770has a bevel 772 formed thereon to limit motion between the upper andlower supports. Annular flange 771 has a bevel 773 formed thereon tolimit motion between the upper and lower supports. Bevel 772 and bevel773 can be inclined so as to avoid point loading when the upper andlower supports are a the maximum angle of inclination. Annular flange770 and annular flange 771 can extend into annular channel 701 to retainthe core. In some embodiments, the plates as described above include anupper retention ring and a lower retention ring with each of the upperand lower retention rings shaped to engage an annular channel of thecore so as to retain the core between the plates.

Retention ring gear 716 can have an annular shape formed to mate withprotruding structure 725. Protruding structure 725 can include an outercircular surface that mates with an inner surface of inner annularsurface of retention ring gear 716. Retention ring gear 716 can rotatearound protruding structure 725. In addition to inwardly protrudingannular flange 770 that retains shock absorbing biconvex core 706,protruding structure 725 can include a retention element 775 such as anoutwardly protruding annular flange and/or C-ring clip to retainretention ring gear 716.

Retention ring gear 718 can also have an annular shape formed to matewith protruding structure 735. Protruding structure 735 can include anouter circular surface that mates with an inner annular surface ofretention ring gear 718. Retention ring gear 718 can rotate aroundprotruding structure 735. In addition to an inwardly protruding annularflange that retains shock absorbing biconvex core 706, protrudingstructure 735 can include an outwardly protruding retention element 775such as an annular flange and/or C-ring clip to retain retention ringgear 718.

Implant 700 can include structures that pivot while the upper and lowersupports are formed. A pivot gear 727 can engage upper retention ringgear 716. Pivot gear 727 is connected to joint 726 so that rotation ofpivot gear 727 rotates pivot joint 726 to rotate distal component 720. Apivot joint 728 connects proximal component 722 to middle component 724of upper support 702. Rotation about pivot joint 728 pivots middlecomponent 724 toward the deployed position. A pivot gear 737 can engagelower retention ring gear 718. Pivot gear 737 is connected to pivotjoint 736 so that rotation of pivot gear 737 rotates pivot joint 736 torotate distal component 704 toward the deployed position. A pivot joint738 connects proximal component 732 to middle component 734 of lowersupport 704. Rotation about pivot joint 738 pivots middle component 734toward the deployed position.

Wedge 832, upper flange 836 and lower flange 838 restrain motion of thejoint assembly during deployment by clamping the joint assembly whilethe joint assembly is advanced. Wedge 832 is positioned between uppersupport 702 and lower support 704. Wedge 832 and upper flange 836 engageproximal component 722 of upper support 702. Wedge 832 and lower flange838 engage proximal component 732 of lower support 704. Advancement ofinner cartridge part 830 advances wedge 832, upper, the upper and lowersupports distally to engage gears of the support.

In many embodiments, the shock absorbing core can be compressed with aninstrument during insertion to allow for a lower profile duringinsertion. For example, casing 810 of cartridge 800 can be sized tocompress the core during insertion so as to lower the profile of thecore. The core can also be compressed during insertion through a tube,sleeve, or the like such that core assumes a low profile compressedconfiguration during insertion so as to minimize the invasiveness of theprocedure, for example with a posterior lateral Wiltse approach asdescribed in U.S. application Ser. No. 11/787,110, entitled “PosteriorSpinal Device and Method”, filed Apr. 12, 2007, the full disclosure ofwhich has previously been incorporated herein by reference. In someembodiments, the core and/or prosthesis can be compressed with forcepswhile inserted into the intervertebral space.

While the exemplary embodiments have been described in some detail, byway of example and for clarity of understanding, those of skill in theart will recognize that a variety of modifications, adaptations, andchanges may be employed. Hence, the scope of the present inventionshould be limited solely by the appended claims.

What is claimed is:
 1. An intervertebral disc prosthesis systemcomprising: a plurality of selectable cores, each core comprising, upperand lower bearing surfaces and a lateral surface between the upper andlower surfaces, each of the selectable cores having differing heightsbetween the upper and lower bearing surfaces; and first and secondsupports locatable about the core, each support comprising, an outersurface which engages a vertebra, and an inner bearing surface shaped tocontact one of the bearing surfaces of each core; and a retainingformation which holds the core captive between the first and secondsupports, wherein the retaining formation includes two or moregroove-like recesses spaced apart about the periphery of the selectablecore and two or more inwardly directed pegs or pins on the first plate,wherein each peg or pin opposing a spaced recess; wherein the upper andlower supports are adapted to articulate with respect to one another andthe core when one of the cores is selected and positioned between thefirst and second supports.
 2. The system of claim 1, wherein each coreis identifiable with an indicia, such that each core is selectable inresponse to the indicia and a patient characteristic.
 3. The system ofclaim 2, wherein the indicia comprises at least one of a color of thecore or a marking on the core.
 4. The system of claim 1, wherein thelower surface of each core is capable of attachment to the firstsupport.
 5. The system of claim 1, wherein the plurality of selectablecores comprises cores with a maximum compression within a range fromabout 0 mm to about 1 mm.
 6. The system of claim 1, wherein the spacedrecesses are formed in the lateral surfaces of the core.
 7. The systemof claim 6, wherein the spaced recesses extend radially inward from thelateral surfaces of the core.
 8. The system of claim 1, wherein theretaining formation allows anterior, posterior and lateral motion of thecore with respect to the first and second plates.
 9. The system of claim1, wherein the pegs or pins are configured to extend into the recessesduring sliding motion of the plates over the core.
 10. The system ofclaim 1, wherein the selectable cores each include at least onespherical bearing surface.
 11. The system of claim 1, wherein theselectable cores have a substantially circular perimeter.
 12. The systemof claim 1, wherein the selectable cores are formed of a resilientmaterial comprising a polymer.
 13. A method of assembling anintervertebral prosthesis for insertion into a patient, the methodcomprising: selecting a core from among a plurality of selectable corescomprising, upper and lower bearing surfaces and a lateral surfacebetween the upper and lower surfaces, each of the selectable coreshaving differing heights between the upper and lower bearing surfacesand each of the selectable cores having two or more groove-like recessesspaced apart about the periphery of the selectable core; placing theselected core between first and second supports; holding the selectedcore captive between the first and second supports with a retainingformation which includes the two or more groove-like recesses spacedapart about the periphery of the selected core and two or more inwardlydirected pegs or pins on the first plate each peg or pin opposing aspaced recess; and allowing the upper and lower supports to articulatewith respect to the selected core when the selected core is positionedbetween the first and second supports.
 14. The method of claim 13,wherein the plurality of selectable cores are identified with an indiciaand the selected core is selected in response to the indicia and apatient characteristic.
 15. The method of claim 14, wherein the indiciacomprises at least one of a color of the core or a marking on the core.16. The method of claim 13, wherein selected core locks into placewithin the first plate or the second plate.
 17. The method of claim 13,wherein the selected core is positioned between the upper support andthe lower support when the upper support and the lower support areinserted into the intervertebral space.
 18. The method of claim 13,wherein the first support and the second support articulate with respectto the selected core when the first support and the second support areinserted into the intervertebral space.
 19. The method of claim 13,wherein the intervertebral prosthesis including the first and secondsupports and the selected core are connected to an insertion device witha grasping member.
 20. The method of claim 19, wherein the graspingmember is configured to allow the intervertebral prosthesis to beinserted under constraint.
 21. The method of claim 13, wherein theretaining formation allows anterior, posterior and lateral motion of theselected core with respect to the first and second plates.
 22. Themethod of claim 13, wherein the pegs or pins are configured to extendinto the recesses during sliding motion of the plates over the selectedcore.
 23. The method of claim 13, wherein the recesses are formed in thelateral surfaces of the selectable cores.